Invisible to a human eye barcodes and other secret insignia are known in the art. They are used for identification and authentication of documents, products, and packages. Such invisible information is printed with inks based on photoluminescent dyes or pigments. Graphics printed with such materials do not selectively reflect, absorb or emit light in the visible spectrum at power level sufficient for detection by unaided eye, therefore are invisible to people.
For viewing invisibly printed insignia and reading invisible barcodes various devices are known in the art, such as those described in the U.S. Pat. Nos. 5,959,296, 6,857,573, 7,516,899, 7,712,667, the disclosures of which are incorporated by reference in their entireties. The known in the art devices for reading invisible insignia, including barcodes, are based on image sensors having spectral sensitivity that stretches beyond the visible spectrum of 370 nm to 690 nm. The other known approach is using fluorescent compounds that emit on visible wavelengths when excited by the energy outside the visible spectrum such as ultraviolet or infrared. For example, the apparatus described in U.S. Pat. No. 7,966,267, the disclosure of which is incorporated by reference in its entirety, for authenticating various articles uses a UV light source. In order to utilize information presented by the invisible insignia the special devices are needed. These devices perform the following functions: image acquisition, recognition, evaluation, barcode decoding, saving encoded data, and communicating it to a different site. Such devices comprise an illumination light source having specific excitation bandwidth, image sensor equipped with special optical filter, and microprocessor for system control, data processing and communications. High cost associated with complexity and sophistication of the invisible insignia acquisition and processing devices often precludes implementation of the invisible barcodes and other invisible insignia technology. Thus, the need exists for a way to enable the sophisticated and ubiquitous products such as smartphones to read the invisibly printed barcodes and other insignia.
Known in the art is use of ubiquitous smartphones for reading visible barcodes such as QR-code, Datamatrix, linear barcodes, and other machine readable insignia. Smartphones also can process information and communicate over USB or wireless ports. However, the smartphones are not capable of acquiring image of barcodes invisible to people. Thus, a need exists for a method and a system making possible reading invisible barcodes and acquiring other secret insignia with the smartphones using only the hardware means already built into the smartphones.
A roadblock for implementing the common approach for acquiring invisible insignia and reading invisible barcodes with the smartphones is the presence of a special optical filter in the smartphone camera optical path that limits its spectral sensitivity exclusively to the visible range. This measure is necessary for proper operation of the solid state high resolution color image sensors built into the smartphones.
The built-in illuminating LED of the smartphones emits only visible light for taking pictures in low light situations. The white illuminating LED does not emit ultraviolet or near infrared energy. This condition excludes using typical invisible inks based on fluorophores producing the Stock or anti-Stock wavelength shift.